A Tour around Dental Implants

(Date of publication 12 September 2005)

Attempts have been made to replace missing teeth with implants for thousands of years, originally with materials such as shells, animal bone and ivory. Have a look at this mandible from about 600 BC – treatment probably left something to be desired in the comfort department! Nowadays, dental implants are a well-established and successful therapy, capable of supporting extensive bridgework and full dentures. One wonders if the proud possessor of the restorations in this X-ray ever has difficulty in getting through airport security...

The American Academy of Periodontology provides some good basic information, pointing out that implants can replace one or more missing teeth without interfering with those adjacent to the space, can support a bridge, eliminate the need for a removable partial denture, or make a denture more stable. There are two main types: endosteal (endosseous), which are actually embedded in the jawbone, and subperiosteal, which lie on the surface of the bone and have extensions protruding through the gingivae (gum) to support a restoration. Endosseous implants may be similar in shape and size to a natural tooth root (root-form) or blade-shaped (plate-form). The different types, and the circumstances in which they are used, are described here, accompanied by clear diagrams.

Most implants are of the root-form endosseous type, and the treatment procedure is outlined on this page. Initially, the implant site is prepared and the implant placed. The gum is then sutured over the top and the jaw is usually left to heal for a period of several months. During this time the bone becomes fused to the implant by a process known as osseointegration. The implant is then re-exposed and a component known as an abutment, which protrudes through the gum to support the final restoration, is attached to it. Impressions are taken and the bridge or denture then constructed. In about 5% of implants rejection occurs, and this complication is more frequent in smokers. However, 90% are still functional after 5 years and more than 75% survive for more than 10 years. The entire procedure can be viewed step by step in this series of photographs (probably not for the squeamish). Techniques vary from one practitioner to the next and in this case a temporary gingival cuff is placed on re-exposure, rather than an abutment.

Most implants are made of titanium, and the process of osseointegration with living tissue is not fully understood. The thin layer of titanium oxide formed on the surface in atmospheric conditions is more extensive when the metal is exposed to biological tissues. Inflammatory cells may contribute to the development of this layer. For those with a background in biochemistry, it has been postulated that the actual interface is a hydrated titanium peroxy matrix, while recent research indicates that matrix metalloproteinases are closely involved.

In attempts to increase the strength of attachment, the machined surfaces of pure titanium and titanium alloy implants have been altered by adding rough titanium coatings, acid etching and grit blasting. Other manufacturers have coated their products with calcium hydroxyapatite (HA), a natural ceramic that occurs abundantly in tooth enamel, dentine and bone. It has been reported that HA-coated implants integrate more rapidly than those that are non-coated but that they are associated with a higher incidence of rejection, and their use remains controversial. However, one study of more than 2,900 implants found that although statistically significant differences were found between the two types, these were too small to be clinically important.

Under certain circumstances it is possible to construct temporary bridges or dentures beforehand and fit them at the same appointment that the implants are placed – a technique known as immediate loading. The permanent restoration is constructed later, at the end of the healing period. This approach is particularly suitable when a front tooth is involved, or the patient is unwilling to wear a removable denture. The immediate replacement of an upper central incisor in this slide show provides a very clear illustration of the various stages, including the excellent aesthetic appearance once treatment is complete. To see what is possible in a more extensive case, look at the before and after photographs of this full upper arch restoration. The patient's severe gag reflex rendered her unable to wear a full upper denture as a temporary measure during the healing period, necessitating immediate loading.

Subperiosteal implants are most commonly used in the lower jaw when no teeth are present and there is insufficient bone height to accommodate endosseous implants. As they are not anchored inside the bone but rest upon it, they are not normally considered to be osseointegrated. Here is a photograph of a subperiosteal implant complete with HA coating of the portion which contacts bone. Nowadays, it is possible to create a model of the patient's jawbone from a CT scan and construct a customised implant on that, rather than taking a direct impression after exposing the bone, so that only one surgical stage is required. Here is an X-ray of the implant in position, and this photograph shows what is visible in the patient's mouth to retain a lower denture.

Implants now have higher success rates than conventional treatment, so if the dental surgeon considers them appropriate, what is the disadvantage? In a word, expense. You may have already noticed that the cost of a single endosseous implant in the US is around $1,600 and a full mouth reconstruction can run to tens of thousands of dollars. For those of us in the UK, it appears to be even more expensive, at £1,500 to £2,000 per tooth. Paying the bill, however, should be the most painful part of the procedure.

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